Frink is a calculating tool and programming language designed to help you in the real world. It tracks units of measurement throughout all
calculations and ensures that answers are correct. It converts between systems of measurement, and has a huge library of physical
data. It is both a simple calculator for quick calculations and a full-fledged programming language for large tasks. It draws high-quality graphics, handles conversions between time zones, currencies, and historical values of the U.S. dollar and the British pound, translates between several languages, does date/time math, and more.

Celestia is an OpenGL-based 3D space simulation for Unix and Win32 that lets you travel through the solar system, to the stars, and even beyond the galaxy. Visit over 100,000 stars, 100 solar system bodies, and all known extrasolar planets.

SaVi is satellite visualization software that lets you create, run, examine, and modify satellite orbits in two and three dimensions. Simulations of Iridium, Globalstar, Galileo, GPS, and other satellite constellations are included. SaVi requires Tcl and Tk on a system with Unix libraries. SaVi works well with the 3D renderer Geomview. Geomview is optional, though recommended for its 3D rendering capabilities.

Xplanet was inspired by Xearth, which renders an
image of the earth into the X root window. All of
the major planets and most satellites can be
drawn, similar to JPL's Solar System Simulator. A
number of different map projections are also
supported, including azimuthal, Mercator,
Mollweide, orthographic, and rectangular.

INDI is an instrument-neutral distributed
interface control protocol that aims to provide
backend driver support and automation for a wide
range of astronomical devices (telescopes,
focusers, CCDs, etc.). Current supported devices
include many telescopes, CCDs, filter wheels,
focusers, and video cams. INDI is used in popular
astronomy suites like Xephem, KStars, DCD, and Cartes
Du Ciel.

TRIP is a general computer algebra system dedicated to celestial mechanics. It includes a numerical kernel and has interfaces to gnuplot and xmgrace. Computations can be performed with double, quadruple, or multi-precision. Users can dynamically load external libraries written in C, C++, or Fortran. Parallel computations on multivariate polynomials can be performed.

Cactus is a general, modular, parallel environment for solving systems of partial differential
equations. The code has been developed over many years by a large international
collaboration of numerical relativity and computational science research groups and can
be used to provide a portable platform for solving any system of partial differential
equations.

Gpredict is a real time satellite tracking and orbit prediction program. Besides the general orbital data for satellites, gpredict can also calculate the footprint, visibility, doppler shift, signal loss, and signal delay for each satellite relative to one or more ground stations. The calculated data can be viewed in tables, on maps, or on polar graphs.